The mechanisms of color, opacifying, and cracks in celadon glazes from the Southern Song Guan Kiln

Guan ware celadon from the Southern Song Dynasty is renowned for its distinctive glaze appearance. This study applied a multi-technique analysis to systematically integrate the chemical composition, iron occurrence form, physical structure, microscopic morphology, and thermal property, explaining the formation mechanism of color, opacifying, and cracks for Guan ware celadon. The result indicated that some glazes were dominated by chemical coloring (the structure of the chromogenic coordination group about iron), influenced by K2O, CaO, and the firing atmosphere. The opacifying resulted from the increase in the light scattering path, which was due to the crystals, abundant bubbles caused by the calcium-alkali type and thick glaze processes, and the structure of nanoscale phase separation. The cracks were mainly attributable to the bigger coefficient of thermal expansion in the glaze, associated with its composition (higher CaO, lower Al2O3). Moreover, the stress effect was further amplified by the thin body and thick glaze.